Britain's waterways turning 'healthy' brown

A new study has revealed that Britain's rivers and streams are much healthier, if less aesthetically pleasing, than they were two decades ago. The change has been linked with the decline of acid rain since the 1970s, clearing up a riddle that has puzzled researchers for some time. But researchers warn that similar work in the future will be impossible, because of proposed cuts in government funding.

Along with other waterways in the industrialised Northern hemisphere, our rivers are now twice as brown as they were in the 1990s, and are returning to a pre-industrialised state, according to the research, published in Nature.

Don Monteith, Senior Research Fellow at UCL says: "A huge amount of carbon is stored in the form of organic deposits in soils, and particularly in the peatlands that surround many of our remote surface waters. Some studies have suggested that we're seeing an unprecedented phenomenon as soils destabilise with unpredictable consequences for the global carbon cycle."

The change has been noticed before, but has variously been attributed to global warming or changing land use. But now, thanks to detailed analysis of more than 500 water samples from across the northern hemisphere, the researchers have tracked down the cause.

John Stoddard of the Environmental Protection Agency says: "We've found that the dominant factor in the whole process is not global warming. The most important driver has actually been the major reduction in acid rain since the 1970s."

He explained that as less acid rain falls, the pH of the soil increases, making carbon more soluble. This means more of it can move into lakes, rivers and eventually, the oceans. The full implications of the process are not clear, he added.

For example, cloudier water means less sunlight penetrating to deeper regions of lakes and riverbeds. This means less plant life in these areas. It is also unclear what will happen to the carbon once it is washed out to sea. the researchers say that it could fall to the ocean floor as sediment, or it could be released as CO2.

Of perhaps more concern is that the movements of heavy metal pollution is closely linked to carbon in water. The researchers say more work is needed to determine how increasing the amount of dissolved organic carbon will affect the environmental pathways of toxins such as aluminium and mercury.

Finally, water companies are unlikely to be pleased by the news. Consumers tend to be suspicious of colour in their water supply, and removing it is a difficult and expensive process. As the rivers recover from the acid rain, keeping the water supply looking pretty looks set to become a bigger problem. ®